General illumination fluorescent lamp which accents the color of green objects

ABSTRACT

Low-pressure fluorescent lamp emits a wide range of visible radiations which provide good color rendition of all illuminated objects, while simultaneously accentuating the color of green objects. This is accomplished by utilizing a phosphor blend of a broad-band-emitting phosphor which peaks in the blue, a broadband-emitting phosphor which peaks in the orange, and a narrowband-emitting phosphor which peaks in the green.

United States Patent [1 1 Halt [ 1 July 24, 1973 GENERAL ILLUMINATION FLUORESCENT LAMP WHICH ACCENTS THE COLOR OF GREEN OBJECTS [75] Inventor: Harry H. Hait, Whippany, NJ.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Sept. 10, 1971 [21] Appl. No.2 179,354

Related US. Application Data [63] Continuation-impart of Ser. No. 12,705, Feb. 19,

1970, abandoned.

[52] US. Cl. 313/109, 313/184 [51] Int. Cl. H0lj 1/63 [58] Field of Search 313/109, 184

[56] References Cited UNITED STATES PATENTS 3,602,758 8/1971 Thornton et al 313/109 3,287,586 11/1966 Bickford ..313/109 Primary Examiner-Roy Lake Assistant Examiner-James B. Mullins Attorney A. T. Stratton and W. D. Palmer et al.

[57] ABSTRACT Low-pressure fluorescent lamp emits a wide range of visible radiations which provide good color rendition of all illuminated objects, while simultaneously accentuat' ing the color of green objects. This is accomplished by utilizing a phosphor blend of a broad-band-emitting phosphor which peaks in the blue, a broad-bandemitting phosphor which peaks in the orange, and a narrow-band-emitting phosphor which peaks in the green.

4 Claims, 7 Drawing Figures FIG.3.

RELATIVE ENERGY WAVELENGTH (nm) (Sr Mg) (PO4) ZSn FIG.4. 4o-

RELATIVE ENERGY WAVELENGTH (nm) Zn SiO4ZMn FIGS RELATIVE ENERGY l I I 400 450 500 550 600 650 700 WAVELENGTH (nm) GENERAL ILLUMINATION FLUORESCENT LAMP WHICH ACCENTS THE COLOR OF GREEN OBJECTS CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of nowabandoned copending application Ser. No. 12,705, filed Feb. 19, 1970 by the present applicant, and owned by the same assignee.

BACKGROUND OF THE INVENTION Fluorescent lamps are normally designed to provide a specific color, such as cool white for example, while simultaneously providing maximum lumens. The most commonly used phosphors are of the so-called halophosphate type. For some applications, the illumination of green colored objects is not as good as desired, and while it is possible to utilize larger amounts of green-emitting phosphor to improve the color appearance of green objects, the color of the resulting overall lamp emission will then have a greenish cast, which makes the lamp unacceptable. An example of an application where the use of a green accentuating lamp would be desirable, provided the disadvantage of an unnatural color appearance for all other illuminated objects could be overcome, is a vegetable counter in a supermarket.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a fluorescent lamp which emits a wide range of visible radiations to provide a good color rendition of all illuminated objects, while simultaneously accentuating the color of green objects. The lamp comprises the usual radiation-transmitting envelope, which has electrodes disposed proximate the ends thereof, and encloses a small charge of mercury and inert ionizable gas. A phosphor coating is carried on the interior surface of the envelope and principally comprises a blend of three different phosphors. The first of these phosphors has an emission peak at from about 610 nm to 650 nm and a broad band emission which has a bandwidth of more than 100 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity of the phosphor. A second of the phosphors has an emission peak at from about 435 nm to 500 nm and a broad band emission having a bandwidth of more than 100 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity of the phosphor. The third phosphor component has an emission peak at about 510 nm to 540 nm and a narrow band emission having a bandwidth of less than 50 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity of the phosphor. The proportions of the phosphor components of the blend are predetermined in order to provide a desired color of the composite emission, such as cool white. The broad band emission of the long wavelength emitting phosphor, coupled with the broad band emission of the short wavelength emitting phosphor and the narrow band emission of the green-emitting phosphor causes the color of all objects illuminated by the lamp to be accurately represented, while simultanteously accentuating the color of green objects.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be had to the exemplary embodiment shown in the accompanying drawings in which:

FIG. 1 is an elevational view, partly broken away, illustrating a fluorescent lamp which incorporates a phosphor blend in accordance with the present invention;

FIG. 2 is a graph of relative energy versus wavelength illustrating the emission of the short wavelength emitting phosphor which comprises a component of the phosphor blend;

FIG. 3 is a graph of relative energy versus wavelength showing the emission of the long wavelength emitting phosphor which comprises another component of the phosphor blend;

FIG. 4 is a graph of relative energy versus wavelength showing the emission of the narrow-band-emitting green phosphor which is used in the composite blend;

FIG. 5 is a graph of relative energy versus wavelength showing the composite emission of the lamp.

FIG. 6 is a graph of relative energy versus wavelength showing the emission of an alternative short wavelength emitting phosphor which can be used as this component of the phosphor blend; and

FIG. 7 is a graph of relative energy versus wavelength showing the emission of an alternative narrow-bandemitting green phosphor which can be used as this component of the phosphor blend.

DESCRIPTION OF THE PREFERRED EMBODIMENTS with specific reference to the form of the invention illustrated in the drawings, the numeral 10 in FIG. 1 indicates a fluorescent lamp comprising a tubular, vitreous, light-transmitting envelope l2 coated internally with a blend of phosphor 14 in accordance with the present invention. Sealed at each end of the envelope 12 are mounts, each comprising an electrode 16, reentrant stem press 18, and lead-in conductors 20. Base caps 22 and base pins 24 are provided at the envelope ends. The envelope contains a small charge of mercury 26 and an inert, ionizable starting gas such as argon at a pressure of 3 torts for example. Except for the phosphor coating, the construction of the lamp 10 is conventional.

Referring to FIG. 2, there is illustrated the spectral energy distribution for a calcium tungstate phosphor which is one preferred short wavelength emitting phosphor component of the blend. In this figure and in FIGS. 3, 4, 6, and 7 all relative energies are normalized to a value of 100. The calcium tungstate peaks at about 400 nm and at an emission intensity which is 50 percent of the maximum measured emission intensity, the bandwidth of the phosphor is about nm. Such a phosphor is known in the art and can be prepared by blending one mole of calcium oxide with 1 mole tungstic oxide (W0 and 0.01 mole lead oxide (PbO), with the resulting raw-mix beinG fired at a temperature of l,l00 C in an air atmosphere for approximately 1 hour. Thereafter the resulting phosphor is lightly crushed to finely divided form prior to use. For the short wavelength emitting component of the blend, it has been found that the emission peak should be from about 435 nm to 500 nm, and in order to provide the proper broad bandwidth, the emission intensity as measured at 50 percent of the maximum phosphor emission intensity should have a bandwidth of more than 100 In FIG. 3 is shown the spectral energy emission for strontium-magnesium orthophosphate activated by tin. Such a phosphor has an emission which appears orange and an emission peak at a wavelength of approximately 630 nm. The emission bandwidth is such that at an emission intensity which is 50 percent of the maximum phosphor emission intensity, the bandwidth is approximately 135 nm. Such a phosphor can be readily prepared by mixing 6.5 moles strontium oxide with 3.5 moles phosphorous pentoxide, 0.3 mole magnesium oxide and 0.2 mole stannous oxide. The mixture is fired in a slightly reducing atmosphere such as nitrogen with 2 percent hydrogen for about 3 hours at approximately l,200 C in covered crucibles. In order to be usable in the present blends,.such a long wavelength emitting phosphor should have an emission peak of from about 610 nm to 650 nm and a broad band emission having a bandwidth of more than 100 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity of the phosphor.

Referring to FIG. 4, there is illustrated the spectral distribution for manganese-activated zinc silicate phosphor, This phosphor has an emission peak at approximately 530 nm and a narrow bandwidth such that at 50 percent of the maximum measured emission intensity, the bandwidth of the phosphor is approximately 45 nm. Such a phosphor can be prepared by mixing 700 grams zinc oxide with 300 grams silicon dioxide and 30 grams manganous carbonate. For best results there is also included with the phosphor raw mix approximately 2 grams of plumbous fluoride and a 0.01 gram arsenic trioxide. The resulting raw mix is fired in an air atmosphere for approximately 3 hours at about 1,300 C in covered crucibles. Other phosphors can be substituted for the preferred zinc silicate provided they have an emission which peaks at from about 51 nm to 540 nm and have a narrow band emission with a bandwidth of less than 50 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity for the phosphor.

After preparation, the foregoing phosphors are mixed in predetermined proportions which are selected to provide a desired color for the composite emission from the lamp. As an example, the relative weight proportions of the orthophosphate, tungstate and silicate are in the approximate ratio of 69:19:12 and in FIG. 5 is shown the composite emission for a 40 watt fluorescent lamp which incorporates approximately 8 grams of the phosphor. The sharp peaks as shown in this figure are due to mercury resonant radiations, which con tribute very little to the overall lamp emission. The continuous band emission output, as shown in FIG. 5, provides good illumination throughout the visible spec trum, in order that all objects which are illuminated by the lamp will be accurately represented, while simultaneously there is an emission peak at approximately 530 nm due to the sharply peaking zinc silicate which is blended with the other broad-band-emitting phosphors.

The color of the resulting lamp which incorporates the foregoing specific blend approximates that of a socalled cool white fluorescent lamp. It has been found that for the specific phosphors as outlined hereinbefore, the orthophosphate desirably is present in amount of from 64 percent to 74 percent by weight of the total phosphor the tungstate in amount of from 15 percent to 25 percent by weight of the total phosphor. and the silicate in amount of from 10 percent to 15 percent by weight of the total phosphor, in order that the color of the resulting lamp will approximate the appearance of the usual fluorescent lamps. In this manner, there has been provided a lamp which accentuates the color of green objects while simultaneously providing good color rendition of all objects illuminated thereby, as well as providing a lighted appearance which closely approximates adajcent lamps which are not tailored to accentuate any particular color.

Other known phosphor materials can be substituted for the individual constituents of the foregoing preferred blend of phosphors. For example, a so-called blue halophosphate can be substituted for the calcium tungstate constituent of the blend and the spectral energy distribution of this blue halophosphate phosphor is shown in FIG. 6. This phosphor has an emission peak at about 480 nm, and at an emission intensity which is percent of the maximum measured emission intensity, the bandwidth of the phosphor is about 127 nm. Such a phospher can be prepared by mixing the following constituents in the following molar proportions: Calcium pyrophosphate, 1.5 moles; calcium carbonate, 1.275 moles; calcium fluoride, 0.45 moles; cadmium oxide, 0.05 mole; and antimony trioxide 0.015 mole. This mixture is fired in a covered crucible at about 1,200 C for about 3 hours, the fired material is then lightly crushed, washed with a dilute solution of nitric acid, water rinsed and dried. A blend which utilized this phosphor, desirably comprises from 58 percent to 68 percent by weight of the foregoing strontiummagnesium orthophosphate, from 6 percent to 11 percent by weight of the foregoing zinc silicate, and from 24 percent to 34 percent by weight of the foregoing blue halophosphate. A preferred example comprises 63 percent by weight of the orthophosphate, 8 percent by weight of the zinc silicate, and 29 percent by weight of the blue halophosphate.

As another example, manganese-activated zinc magnesium silico-germanate can be substituted for the zinc silicate in the foregoing blend, with the proportions of the silicogermanate in the blend being approximately the same as the zinc silicate which it replaces. This phosphor has an emission peak at about 535 nm, and at an emission intensity which is 50 percent of the maximum measured emission intensity, the bandwidth of the phosphor is about 45 nm. Such a phosphor is prepared by mixing the following constituents in the following molar proportions: 1.7 moles zinc oxide, 0.3 mole magnesium fluoride, 0.6 mole germanium dioxide, 5 X 10 mole arsenic trioxide, and '4 X 10* mole lead oxide (PbO). The raw-mix is fired for 2 hours in air at 1,200 C, lightly ground and then retired for 1 hour in a nitrogen atmosphere at l,l00 C.

As another example, strontium-zinc orthophosphate activated by stannous tin, which is a known phosphor, can be substituted for the foregoing strontiummagnesium orthophosphate in the foregoing blend examples.

The foregoing phosphor species which are used to form the blends can also be mixed. As an example, the blue halophosphate can be mixed with the calcium tungstate in equal weight amounts. The resulting preferred blend will then comprise 66 percent by weight strontium-magnesium orthophosphate, 10 percent by weight zinc silicate, 12 percent by weight calcium tungstate, and 12 percent by weight of blue halophosphate.

While the present phosphor blend principally comprises three major phosphor components as described hereinbefore, it should be understood that small amounts of other phosphors may also be included in the blend, such as for special color rendition effects. For example, the blend could also include two percent by weight of any known long wavelength emitting phosphor or a short wavelength emitting phosphor.

I claim:

1. A fluorescent lamp which emits a wide range of visible radiations to provide good color rendition of all objects illuminated thereby while simultaneously ac-i centuating the color of green objects, said lamp comprising:

a. a sealed radiation-transmitting envelope having electrodes disposed proximate the ends thereof and enclosing a small charge of mercury and inert ionizable gas; and

b. a phosphor coating carried on the interior surface of said envelope, said phosphor coating principally comprising a blend of three different phosphors, a first of said phosphors is tin-activated strontiummagnesium orthophosphate having an emission peak at from about 610 nm to 650 nm and a broad band emission having a bandwidth of more than 100 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity thereof, a second of said phosphors is calcium tungstate having anemission peak at from about 435 nm to 500 nm and a broad band emission having a bandwidth of more than 100 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity thereof, and the third of said phosphors is maganese-activated zinc silicate having an emission peak at from about 510 nm tp 540 nm and a narrow band emission having a bandwidth of less than 50 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity thereof, and said phosphors being present in the following predetermined proportions to provide the desired color oj composite emission, said orthophosphate is present in amount of from 64 percent to 74 percent by weight of total phosphor, said tungstate is present in amount of from 15 percent to 25 percent by weight of total phosphor, and said silicate is present in amount of from percent to percent by weight of said total phosphor, whereby the narrow band emission of said third phosphor causes the color of green objects illuminated by said lap to be accentuated while simultaneously the color of all objects illuminated by said lamp is accurately displayed due to the broad band emissions of said first and second phosphors.

2. The lamp as specified in claim 1, wherein the relative weight proportions of said orthophosphate, said tungstate and said silicate are approximately 69:19:12.

3. A fluorescent lamp which emits a wide range of visible radiations to provide good color rendition of all objects illuminated thereby while simultaneously accentuating the color of green objects, said lamp comprising:

a. sealed radiation-transmitting envelope having electrodes disposed proximate the ends thereof and enclosing a small charge of mercury and inert ioniz able gas; and

b. a phosphor coating carried on the interior surface of said envelope, said phosphor caoting principally comprising a blend of three different phosphors, a first of said phosphors is tin-activated strontium magnesium orthophosphate having an emission peak at from about 610 nm to 650 nm and a broad band emission having a bandwidth of more than nm as measured at an emmission intensity which is 50 percent of the maximum measured emission intensity thereof, a second of said phosphors is blue halophosphate having an emission peak at from about 435 nm to 500 nm and a broad band emission having a bandwidth of more than 100 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity thereof, and the third of said phosphors is manganese-activated zinc silicate having an emission peak at from about 510 nm to 540 nm and a narrow band emission having a bandwidth of less than 50 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity thereof, and said phosphors being present in the following predetermined proportions to provide the desired color of composite emission, said orthophosphate is present in amount of from 58 percent to 68 percent by weight of total phosphor, said halophosphate is present in amount of from 24 percent to 34 percent by weight of total phosphor, and said silicate is present in amount of from 5 percent to 11 percent by weight of total phosphor, whereby the narrow band emission of said third phosphor causes the color of green objects illuminated by said lamp to be accentuated while simultaneously the color of all objects illuminated by said lamp is accurately displayed due to the broad band emissions of said first and second phosphors.

4. The lamp as specified in claim 11, wherein the relative weight proportion of said orthophosphate, said halophosphate and said silicate are approximately 63:29z8. 

2. The lamp as specified in claim 1, wherein the relative weight proportions of said orthophosphate, said tungstate and said silicate are approximately 69:19:12.
 3. A fluorescent lamp which emits a wide range of visible radiations to provide good color rendition of all objects illuminated thereby while simultaneously accentuating the color of green objects, said lamp comprising: a. sealed radiation-transmitting envelope having electrodes disposed proximate the ends thereof and enclosing a small charge of mercury and inert ionizable gas; and b. a phosphor coating carried on the interior surface of said envelope, said phosphor caoting principally comprising a blend of three different phosphors, a first of said phosphors is tin-activated strontium magnesium orthophosphate having an emission peak at from about 610 nm to 650 nm and a broad band emission having a bandwidth of more than 100 nm as measured at an emmission intensity which is 50 percent of the maximum measured emission intensity thereof, a second of said phosphors is blue halophosphate having an emission peak at from about 435 nm to 500 nm and a broad band emission having a bandwidth of more than 100 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity thereof, and the third of said phosphors is manganese-activated zinc silicate having an emission peak at from about 510 nm to 540 nm and a narrow band emission having a bandwidth of less than 50 nm as measured at an emission intensity which is 50 percent of the maximum measured emission intensity thereof, and said phosphors being present in the following predetermined proportions to provide the desired color of composite emission, said orthophosphate is present in amount of from 58 percent to 68 percent by weight of total phosphor, said halophosphate is present in amount of from 24 percent to 34 percent by weight of total phosphor, and said silicate is present in amount of from 5 percent to 11 percent by weight of total phosphor, whereby the narrow band emission of said third phosphor causes the color of green objects illuminated by said lamp to be accentuated while simultaneously the color of all objects illuminated by said lamp is accurately displayed due to the broad band emissions of said first and second phosphors.
 4. The lamp as specified in claim 11, wherein the relative weight proportion of said orthophosphate, said halophosphate and said sIlicate are approximately 63:29:8. 